A network system has become popular that has a configuration where multiple processing units such as ECUs (Electronic Control Units) and the like are connected with a bus. The multiple ECUs in such a network system execute information processing allocated to the respective units, and are capable of outputting processed results on the bus to provide the results for the other ECUs. Also, in such a network system, a process called a “communication arbitration” may be executed to avoid the multiple ECUs outputting data on the bus at the same time. The communication arbitration is executed in a network system, for example, that executes communications based on a CAN (Controller Area Network). The communication arbitration in a CAN is executed under a rule where each ECU compares data transmitted by itself with a result obtained by monitoring bus states, and if the bus states are compliant with the data transmitted by itself, then the ECU determines that it wins the communication arbitration, and continues to output data.
Also, a system has been disclosed in which various ECUs are connected with a communication bus, and when the multiple ECUs attempt to transmit data in response to transmission requests, transmission data having a higher priority is prioritized to be written in a transmission buffer (see, for example, Patent Document 1).
Also, an apparatus has been disclosed that includes multiple buffer memories, stores digital information to be transmitted in one of the multiple buffer memories depending on types of the digital information to be transmitted, and sets transfer order depending on waiting numbers and priorities accompanying the data, which change along with the progress of the transmission process (see, for example, Patent Document 2).